In an optical communication system, it is generally necessary to couple an optical fiber to an opto-electronic transmitter, receiver or transceiver device and, in turn, to couple the device to an electronic system such as a computer or other processing system. These connections can be facilitated by modularizing the transceiver device. An opto-electronic transceiver module includes an opto-electronic light source, such as a laser, and an opto-electronic light receiver, such as a photodiode, and may also include various electronic circuitry associated with the laser and photodiode. For example, driver circuitry can be included for driving the laser in response to electronic signals received from the electronic system. Likewise, receiver circuitry can be included for processing the signals produced by the photodiode and providing output signals to the electronic system. The electronic and opto-electronic devices can be mounted on a small circuit board or similar substrate inside the transceiver module housing. The circuit board can include electrical contacts or connectors for connecting the opto-electronic transceiver to the external electronic system.
In some modular opto-electronic transceiver systems, an optical plug that terminates an optical fiber cable can be plugged into a socket in the transceiver module housing. When coupled to the transceiver module in this manner, the ends of optical fibers in the plug are optically aligned with optics in the opto-electronic transceiver. The optics couple electronic signals between the fibers and the laser and photodiode. A first fiber, which can be referred to as a transmit fiber, is optically coupled to the laser so that optical signals generated by the transceiver module are transmitted via that transmit fiber. A second fiber, which can be referred to as a receive fiber, is optically coupled to the photodiode so that optical signals received via the receive fiber can be received by the transceiver module.
In some opto-electronic transceiver modules, the optical signal path includes a 90-degree (90°) turn. For example, the above-described circuit board on which the laser and photodiode are mounted can be oriented perpendicularly or normal to the axes along which the optical signals are communicated with the optical fibers in the plug. The laser emits the optical transmit signal in a direction normal to the circuit board, and the photodiode receives the optical receive signal from a direction normal to the circuit board. The above-referenced optics in the transceiver module can include a first lens that collimates the optical transmit signal emitted by the laser and a second lens that focuses the optical receive signal upon the photodiode. A mirror or similar reflective element in the transceiver module can redirect the signals emitted by the laser and received by the photodiode at 90° angles with respect to the circuit board.